Motor control system



Sept. 3, 1946. J. D. LEwis 2,406,782

MOTOR CONTROL SYSTEM Original Filed Nov. 27, 1943 1,1 mm I 2 Sheets-Sheet 1 MST FIG. I gwnwbuw INVENTOR ATTORNEY Sept. 3, 1946. J wfs 2,406,782

MOTOR CONTROL SYSTEM Original Filedlflov 27, 1943 2 Sheets-Sheet 2 v .l 2 .0 4 1------ i; 2 .0 4

x iv idg u i. EJT M fi -1 LT? 5 i} fi &

MIIII law I. rllllalfi s l fi: gfi

- ATTORNEY.

5 i i I i i l i i I I J mflwil Lug INVENTOR llfiiillnllllllmgililll--2, m M=M= .!||||||i|liillliiiilhwg Mqfi a |-||...|%.|||& q? lllll ||=,=.i|||||:|||||||.i| Ii: a. O 2 .o O lilllla. 3%.?

I! lllll 4 5 In 2 2U :fiiillllllllt i: A S .0

l 2 T if FIGQIS Patented Sept. 3, 1946 MOTOR CONTROL SYSTEM Jacob Daniel Lewis, Yonkers, N. Y., assignor to Otis Elevator Company, New York, N. Y., a corporation of New Jersey Original application November 27, 1943, Serial No.

512,023. Divided and this application December 7, 1944, Serial No. 567,085

3 Claims. 1

The invention relates to control systems for electric motors, especially for hoists.

This application is a division of application Serial Number 512,023 of Jacob Daniel Lewis, filed. November 27, 1943.

It is desirable in certain control systems for electric motors to utilize speed responsive means. It is the object of the invention to provide electroresponsive means responsive to the speed of an electric motor.

The invention involves rendering electrore sponsive means subject to a predetermined voltage and a variable voltage dependent upon the speed of the motor.

The invention is especially applicable to control systems for polyphase induction motors. It will be described as applied to such a control system in which the motor is plugged to slow it down, with the speed responsive means arranged to operate when the speed of the motor has been reduced to a certain value.

In carrying out the invention as applied to such a system according to the arrangement which will be described, a control switch has its coil connected across a portion of a potentiometer resistance, the voltage applied to one portion of which is derived from the source of polyphase alternating current for the motor and the voltage applied to the remaining portion of which is derived from the voltage of the rotor of the motor. These applied voltages are direct current voltages obtained from rectifiers connected across the alternating current source and the rotor, the output circuit of the rectifiers being connected in series relation and in opposition. In starting the motor, the coil of the switch is connected to such points on the potentiometer resistance that the voltage derived from the source predominates and causes the operation of the switch. Upon plugging the motor to slow it down, the connections of the coil are reversed and are made to such points on the potentiometer resistance that the voltage derived from the rotor predominates and maintains the switch operated. Astthe motor speed nears zero, the switch drops on The control system illustrated is for a cargo winch. The induction motor serves to lift or lower the hook and is a multi-speed motor. The

control system is arranged to operate the motor I to lower the hook at a slow speed prior to stopping to facilitate landing the cargo. In this system, the speed responsive switch, when it drops out in slowing down the motor, controls the application of the electro-mechanical brake or, if slow speed operation is desired for land ing the cargo, the change-over to slow speed operation.

Features and advantages of the invention will be seen from the above statements and from the following specification and appended claims.

In the drawings:

Figure 1 is a simplified wiring diagram in across-the-line form of a control system for the cargo winch motor; and

Figure 1s is a key diagram for Figure 1 showing the electromagnetic switches in spindle form with the contacts and coils arranged on the spindles in horizontal alignment with the corresponding contacts and coils in the wiring diagram.

The hoisting motor is a three speed, three phase induction motor. These different speeds are obtained by exciting the stator to provide three different numbers of field poles, one pole number for normal speed, a second for fast speed and the remaining for slow speed. In the arrangement illustrated this is effected by providing two windings on the stator, one for a high number of poles for slow speed operation and the other arranged to provide either a number of poles for normal speed operation or a lower number of poles for fast speed operation. The rotor is provided with two windings, one a definite pitch squirrel cage winding and the other phase wound. The latter winding is wound for the number of poles of stator excitation for normal speed. It is connected through slip rings to rotor resistance which may be varied to control the torque of the motor. The pitch of the squirrel cage winding is such that it serves as the rotor winding for both fast speed stator excitation and slow speed stator excitation. The number of poles of stator excitation are so correlated that zero or negligible current flows in the phase wound rotor winding during excitation for either fast or slow speed operation and zero or negligible current flows in the squirrel cage winding during excitation for normal speed operation.

The wiring diagram of Figure 1 illustrates a control system for the above described motor utilized as a cargo winch motor. The circuits are shown in straight or across-the-line form in which the coils and contacts of the electromagnetic switches are separated in such manner as to render the circuits as simple and direct as possible. The relationship of these coils and contacts may be seen from Figure 18 where the switches are arranged in alphabetical order and shown in spindle form, with the coils and contacts aligned horizontally with the coils and contacts which they indicate in the wiring diagram.

The alternating current supply mains are designated I, II and III. A triple pole manually operated main line switch designated ML is provided for controlling the supply of current from the supply mains. The two stator windings of motor are a two speed winding designated MST for providing excitation for normal and fast speed operation, and a single speed winding designated MSS for slow speed operation. The phase wound winding of the rotor is designated MRP while the squirrel cage Winding is designated MRS. The phase wound winding is connected through slip rings E62, M3 and Iii-2 and brushes Bi, B2 and to star connected rotor resistance RR. Direct current for the electromagnetic control switches and release coil B of the brake is derived from the alternating current supply mains through a three phase transformer TI and rectifier REL Another three phase transformer T2 is connected through brushes Bl, B2 and B3 and slip rings I02, I03 and I84 to the phase wound rotor winding of the motor. A three phase rectifier RE? is connected across the secondary of this transformer to provide direct current for controlling the operation of a governor switch. Control resistances utilized in the control system are designated generally as R and diiierentiated by numerals while condensers are designated generally as C and differentiated by numerals. The negative side of the feed wires to the electromagnetic switches is grounded at GR. The master control switch utilized for manually controlling the operation of the motor has its bridging segment designated MS and the stationary contacts engaged thereby designated MUF, MUI, MUZ, MU3, MU l, MU5 and MUS for up travel of the hook, and MDF, MDI, MD2 and MD3 for down travel of the hook. The segment MS is shown with its center part broken away, it being understood that it is long enough to span contacts MUF to MUG, contacts MUF and MDF being spaced so that they are the only ones engaged with the segment in off position. The emergency stop switch which is located adjacent the master controller is designated EM.

The electromagnetic switches have been desig- S Governor switch relay SA Auxiliary governor switch relay SS Slow speed switch U Up direction switch Z }Auxiliary direction switches Throughout the description which follows, these letters will be applied to the coils of the above designated switches. Also, with reference numerals appended thereto they will be applied to the contacts of these switches, as for example U1. The electromagnetic switches are shown in deenergized condition, that is the switch contacts shown separated are those which engage when the switch is operated while those shown engaged are those which separate when the switch is operated.

In addition to the above listed switches there is a load switch designated generally by the letter L. This switch is in the form of a two phase motor operated switch. The two stator phase windings of this motor are designated LC and LP. The rotor of the motor is designated LR. and is adapted to operate an arm LA on the end of which is a contact LM for engaging either of stationary contacts LX or LY. The contact arm LA is biased, as by a weight illustrated as integral with contact LM, to the position shown with contact LM intermediate the stationary contacts. The stationary contacts serve as stops to limit the amount of rotative movement of the rotor.

Assume that the hook is in a low position and that main line switch ML i closed. Under such conditions the circuit for the coil of auxiliary fast speed switch AF is completed so that contacts AFI and AFS are engaged and contacts AFZ are separated. To raise the hook the master switch i operated to move bridging segment MS into position to bridge one or more stationary con tact MUI, M02, MU3, MU4, MU5 and MU5 with feed contact UP. The engagement of segment MS with contact MU! completes a circuit for the coil of up direction switch U. This circuit is from the positive feed line through contacts X2, feed contact MUF, contact MUl, contacts XI, resistance R9, coil of switch U, and contacts D3, to the negative feed line. Switch U, upon operation, separates interlock contacts U4 in the circuit for the coil of down direction switch D. It also engages contacts UI and U2 to establish direction for stator winding MST of the winch motor. It also engages contacts US to complete a circuit for the coil of brake relay BR. Relay BR, upon operation, engages contacts BB3 to effect the energization of the re lease coil of the electromechanical brake B. At the same time it engages contacts BB4 completing a circuit through contacts AF3, SS L, D5 and PS6 for the coil of normal speed switch NS. Switch NS, upon operation, engages contacts NSI, NS2, N83 and NS4 completing a circuit for stator winding MST of the winch motor for normal speed operation. In the arrangement shown, the circuits through contacts NSi, NS?! and N54 lead to mid points I20, HI and !22 of the phase windings so that the two halves of each phase winding thus obtained are connected in parallel to a star point provided by the engagement of contacts N83. The circuit from supply line I to the stator winding is through winding LC of load switch L and contact N84 to connection point I22. The circuit from supply line II is through contacts U2, coil of overload switch OA and contacts NSZ to connection point I29. The circuit from supply line III is through contacts III, the coil of overload switch OB and contacts NSI to connection point l2l. This cause excitation of the stator to provide eight poles, the phase rotation of the applied voltage due to the circuits being through contacts of the up direction switch being such as to cause starting of the winch motor to lift the hook, the brake being released as the result of energization of the brake release coil.

The engagement of contacts BR4 also complete a circuit for the coil of governor switch G. This coil is subject to the voltage of the potentiometer formed by the combination of resistances R3 and R4. Resistance R3 is connected across rectifier REI whereas resistance R4 is connected acros rectifier RE2. The voltage of rectifier REZ is derived from the alternating current voltage of the phase wound winding MRP of the rotor which is effective on eight pole excitation. Also rectifie REZ is connected in opposition to rectifier REI. There are two adjustable points of connection I25 and I26 to resistance R3. The point L26 is adjusted so that the potential drop across the portion of resistance to the right of this point is neutralized by the potential drop across resistance R4 at standstill of the rotor on eight pole excitation. However, the circuit now completed for the coil of switch G is through contacts S3 and S2 to point of connection I25 on resistance R3 that sufficient vcltage is applied to the coil of switch G due to the excess potential drop across the portion of resistance R3 between points I25 and I26 to cause this switch to operate upon the starting of the motor. Switch G, upon operation, engage contacts GI completing a circuit for the coil of auxiliary direction switch Z. This circuit is through contacts X2, coil of switch Z and contacts U3 and GI. Switch Z, upon operation, separates contacts Z! to break the circuit to down feed contact MDF of the master switch and also separates interlock contacts Z3 in circuit for the coil of down direction switch D.

If in starting the motor master switch segment MS is moved only into engagement with contacts MUI, all of rotor resistance RR remains in circuit with the phase Wound rotor winding. However, assume that the master switch segment is moved into position to connect all of the up contacts to feed contact MUF. The engagement of segment MS with contact MU2 completes a circuit through contact AFI for the coil of accelerating switch AA. This switch, upon operation, engages contacts AAI and AAZ to short circuit a portion of the rotor resistance. It also engages contacts AA3 to complete a circuit for causing the operation of accelerating switch BA.

Each of accelerating switches BA, CA and DA have two coils, the lower one an operating coil and the upper one a delaying coil. With main line switch ML closed contacts AFI are in engagement as previously set forth 'so that circuits are completed through condensers in series respectively with both coil of each of these acce1- crating switches. One circuit is through contacts BA3, condenser C5, the delaying coil of switch BA, the operating coil of the switch and contacts AFI. Another circuit is through contacts CA3, condenser C5, the delaying coil of switch CA, the operating coil of the switch and contacts AFI. The remaining circuit is through contact DA3, condenser C4, the delaying coil of switch DA, the operating coil of the switch and contacts AFI. A a result, condensers C4, C5 and C6 are in a charged state prior to the starting of the car.

The engagement of contacts AA3 closes a circuit which connects the operating coil of switch BA to the positive feed line and which Icy-passes condenser C5 and the delaying coil of the switch, thereby completing a discharge circuit for the condenser. This discharge circuit is from the positive feed line through contacts BA3, condenser CS, delaying coil of switch BA, resistance R8, contacts AAS, contact MU3, bridging segment MS, feed contact MUF, contacts X2 back to the positive line. The current flow through the delaying coil of switch BA by the discharge of condenser C6 is in a direction to cause the magnetizing force of the delaying coil to oppose the magnetizing force of the operating coil of the switch. This prevents the immediate operation of switch BA. When the discharge of condenser CG reaches a certain point switch BA operates to engage contacts BAI and BAZ. This short circuits a further portion of rotor resistance RR to increase the torque of the motor. Switch BA also separates contacts BA3 to break the circuit for the delaying coil of the switch and engages contacts BA I to close a circuit connecting the operating coil of accelerating switch CA to the positive feed line and completing a discharge circuit for condenser C5 through the delaying coil of switch CA. The operation of switch CA is thus delayed in the same manner as described for the operation of switch BA. Upon operation, switch CA engages contacts CAI and CA2 to short circuit a further portion of rotor resistance RR to further increase the torque of the motor. It also separates contacts CAI to break the circuit for the delaying coil of the switch and engages contacts CA4 to cause the operation of accelerating switch DA. The operation of switch DA is similarly delayed and upon operation it engages contacts DAI and DA! to short circuit the remainder of the rotor resistance RR to further increase the torque of the motor and separates contacts DA3 to break the circuit for the delaying coil of the switch.

Switch DA, upon operation, also engages contacts DA5 to complete a circuit from master switch contact MUS through resistance RI3 for the coil of auxiliary fast speed switch BF. Switch BF, upon operation, engages contacts BF3 to establish a self-holding circuit. It also separates contacts BFI rendering the coil of auxiliary fast speed switch AF subject to load switch L.

Phase winding LC of the load switch operating motor is connected in series relation in the circuit leading from supply line I to stator winding MST of the winch motor on eight pole excitation. One end of the other phase winding LP is adjustably connected to a potentiometer resistance RI connected across supply lines II and III by the engagement of contacts BRI and BRZ. The other end of phase winding LP is connected to supply line I. The point of connection of phase winding LP to potentiometer resistance RI is such that the current supplied to this winding is substantially in phase with the current in the phase winding LC when the winch motor is operating on eight pole excitation and is up to speed under conditions of empty hook. Under such conditions no torque is exerted by the rotor to move contact LM into engagement with either of stationary contacts LX or LY. With empty hook the rotor may act to move contact LM into engagement with one of the stationary contacts during the accelerating period owing to the fact that a certain amount of load current is drawn by the winch motor for effecting acceleration. However, as soon as the motor is up to speed, the current in winding LC returns to in phase with that in winding LP so that the load operating motor loses its torque and contact LM disengages the stationary contact.

Inasmuch as a condition has been assumed in which the hook is empty, load switch contact LM is disengaged from its stationary contacts as the motor comes up to speed so that with contacts BFI separated the circuit for the coil of auxiliary fast speed switch AF is broken. The dropping out of switch AF is delayed by the discharge of condenser CI to insure that the motor is up to running speed. Upon dropping out, switch AF separates contacts AF! breaking the circuits for the coils of accelerating switches AA, BA, CA and DA and separates contacts AF3 to break the circuit for the coil of normal speed switch NS. Switch NS, upon dropping out, separates contacts NSI, NSZ, NS3 and NS4 to break the circuit for stator winding MST of the driving motor. It also engages contacts NS'I completing a circuit from contact MUG of the master control switch through contacts BFZ, AFZ, SS3 and NS! for the coil of fast speed switch FS. Switch FS, upon operation, separates interlock contacts PS8 in the circuit for the coil of normal speed switch NS and engages contacts FSI, FSZ and FS3 reconnecting stator winding MST of the winch motor to the supply lines in such way that the two halves of each phase winding are connected in series, with the phase windings connected in delta relation. This causes excitation of the stator to provide four poles, which brings the motor from normal operating speed up to fast speed. The squirrel cage rotor winding is effective to provide the torque for fast speed operation. It is to be noted that the circuit from supply line I to the stator winding for fast speed operation does not include winding LC of the load switch operating motor. Thus, the load switch is not subject to the accelerating current of the winch motor in bringing the motor up to fast speed, thereby preventing the operation of the load switch to return the motor to eight pole excitation.

The load switch is adjusted as by means of its biasing weight to prevent the engagement of the movable contact LM with a stationary contact when the load on the winch is light, say below 15% of the rated load. Assume that the hook is being raised and is lifting a heavy load. Under such conditions the rotor LR of the load switch operating motor will have rotated in a certain direction assumed as clockwise to move contact LM into engagement with stationary contact LX.

Thus, although switch BF operates to separate contacts BFI, contact LM remains in engagement with contact LX after the winch motor acceleration on eight pole excitation has been completed so that the circuit for the coil of auxiliary fast speed switch AF is not broken and the winch motor does not change over to fast speed operation.

Should the upward movement of master switch segment MS not be all the way, the winch motor will operate at a speed for the particular load determined by the position to which the master switch segment is moved. Assume for example that the master switch segment is moved only so far as contact MUS. Under such conditions change-over from normal to fast speed operation cannot be made regardless of the load being lifted. If the master switch segment is moved only so far as contact MU I, accelerating switch DA is not operated so that a portion of rotor resistance BB. is not short-circuited, thereby causing the motor to run at a slower speed. A similar condition exists if the master switch segment is moved only so far as contacts MU3, iii [U2 or MUI. Also the motor may be slowed down by moving the master switch segment off the stationary contacts in one or more steps in which case, as above explained, the speed of the winch motor will be determined by the farthest contact with which the master switch segment is engaged.

While the winch motor may be slowed down turn the master switch segment directly to ofi position. Assume that the master switch segment has been moved into full up position engaging contact MUS and that the hook is empty, so that the winch motor is operating at fast speed. The fast speed switch, upon operation to connect stator winding MST for four pole excitation, also engaged contacts FS-l completing a circuit for the coil of auxiliary fast speed switch CF. Switch CF, upon operation, engages contacts CF3 to complete a circuit for the coil of downac celerating fast speed switch DF. Switch CF also engages contacts CFl to establish a holding ci r cuit for the coil of up direction switch U, bypassing the master switch. Thus upon return of the master switch segment to on position switch U is maintained operated.

The disengagement of the master switch segment from contacts MUG as the master switch segment is returned to off position breaks the circuit for the coils of auxiliary fast speed switch BF and fast speed switch FS. Switch BF, upon dropping out, engages contacts BFi to reestabe lish a circuit for auxiliary fast speed switch AF. Switch AF engages contacts AF3 which to ether with the reengagement of contacts FSG of the fast speed switch reestablishes the circuit for the coil of normal speed switch NS. Thus with the fast speed switch dropped out to separate contacts FSI, PS2 and PS3, the normal speed switch operates to reengage contacts NSI, NSZ, NS3 and NS4, thereby restoring the circuits for winch motor stator winding MST to provide eight pole excitation. As a result the winch motor is slowed down by regenerative braking. Switch AF also engages contacts AFI which, owing to the fact that contacts DFI, DFZ, DF3 and DF4 are now engaged, causes the reoperation of accelerating switches AA, BA, CA and DA in se quence, short-circuiting rotor resistance RR in steps to give the desired slow down torque.

The fast speed switch, upon dropping out, also separates contacts FS4 to break the circuit for the coil of auxiliary fast speed switch CF. This switch does not drop out immediately, the discharge of condenser C3 into the coil of the switch delaying the dropping out long enough to permit slowing down of the winch motor to normal speed operation. Upon dropping out, switch CF separates contacts CF3 to break the circuit for the coil of down auxiliary fast speed switch DF, causing this switch to drop out. It also sepa rates contacts CFI, breaking the circuit for the coil of up direction switch U (this circuit being broken by the return of the master switch to off position in case the motor has not been operat ing at fast speed). The up direction switch in dropping out, separates contacts U3, the coil of auxiliary direction switch Z being maintained sufficiently energized by way of the circuit through resistance Rlil to cause this switch to remain operated. The up direction switch also engages contact U4 which completes a circuit for the coils of auxiliary governor switch relay SA and down direction switch D. This circuit is through contacts DA l, CA5 and BA5 now engaged as a result of the dropping out of switch DF (01' by return of the master switch to off position in case the motor had not been operat-. ing at fast speed), coil of relay SA, contacts Z2, coil of switch D and contact U4. As a result, relay SA and switch D operate. Switch D, upon operation, separates interlock contacts D3 in the circuit for the coil of up direction switch U. It

also separates contacts D4 in the circuit for the coil of normal speed switch NS. The circuit for the coil of switch NS is maintained established through contacts Z4 after the separation of contacts D4. Switch D also engages contacts D to reestablish the circuit for the coil of brake relay BR, broken by the separation of contacts U5, this relay being maintained operated by the discharge of condenser 01 into its coil during the interval that is circuit is broken. Switch U, upon dropping out, also separates contacts UI and U2 in the circuits for stator winding MST of the winch motor. However, contacts DI and D2 engage to reestablish the circuits for stator winding MST for eight pole excitation, but reversing the connections to the stator Winding from supply lines II and III. This plugs the winch motor, causing further slow down.

Auxiliary governor switch relay SA, upon operation, engages contacts SAI completing a circuit through contacts NS5 for the coil of governor switch relay S. Relay S, upon operation, separates contacts S2 and S3 and engages contacts SI and S4. This not only renders the coil of governor switch G subject to the portion of potentiometer resistance R3 to the right of point I26 but also reverses the circuit for this coil. As a result of the reversal of the excitation of stator winding MST of the winch motor in plugging the motor the voltage across the slip rings of the phase wound winding of the rotor is increased substantially to twice standstill voltage for eight pole excitation of the motor. As a result the resistance drop across potentiometer resistance R4 is greater than that across the now used portion of resistance R3, thereby reversing the polarity of the voltage applied to the coil of governor switch G. By reversing the circuit for the coil of switch G the current flow through this coil is in the same direction through contacts SI and S4 as it was through contacts S2 and S3 so that switch G does not drop out, switch G being maintained operated during the change of connections by the discharge into its coil of condenser C2.

As the winch motor slows down, the voltage across the slip rings of the rotor decreases with the result that the voltage applied to the coil of switch G decreases. As the voltage drop across the now used portion of resistance R3 is neutralized by the voltage drop across resistance R4 at standstill on eight pole excitation, the voltage applied to the coil of switch G becomes zero as the rotor comes to a stop. Relay G drops out just before the voltage across its coil drops to zero, separating contacts GI. This breaks the circuit for the coil of switch Z, causing this switch to drop out. Upon dropping out, it separates contacts Z2 breaking the circuit for the coils of switch D and relay SA. Switch D, upon dropping out, separates contacts DI and D2 to deenergize stator winding MST of the winch motor and also separtes contacts D5 to break the circuit for the coil of brake relay BR. As contacts G2 ar now separated, relay BR drops out immediately. Relay BR, upon dropping out, separates contacts BR3 to break the circuit for the release coil of electro-mechanical brake B. Thus, the brake is applied to bring the winch motor to a stop. The brake relay also separates contacts BR4 to break the circuit for the coil of normal speed witch NS which drops out. The separation of contacts BR4 also breaks the circuit for the coil of switch G. In the meantime, as the result of the separation of contacts SAI of the auxiliary governor switch relay, auxiliary governor switch S drops 10 out to restore its contacts in circuit with the coil of switch G to the positions illustrated.

To lower the hook, master switch segment MS is moved downwardly to bridge contacts MDI, MDZ and MD3 with feed contact MDF. As in the case of raising the hook, the master switch segment may be moved all the way over or only to an intermediate position. Assume first that the master switch segment is initially moved all the way over to bridge contacts MDl, MDE and MD3 with contact MDF. The bridging of contacts MDF and MDl completes a circuit for the coil of down direction switch D. This circuit is through contacts 2!, contacts MDF and MD l, contacts Z3, resistance Rl2, contacts X4, coil of switch D, and contacts U4. The down direction switch, upon operation, engages contacts DI and D2 to establish direction for the winch motor for downward hook movement and engages contacts D5 to complete the circuit for the coil of brake relay BR. The bridging of contacts MDF and MD2 completes a circuit for the coil of down auxiliary fast speed switch DF. Switch DF, upon operation, separates contacts D-FB to prevent th energization of the coil of slow speed switch SS. It also engages contacts DF8 so that, although contacts D4 separate, the engagement of contacts BR4 completes a circuit for the coil of normal speed switch NS. Switch NS engages contacts NSI, N82, NS3 and NS4 to complete a circuit for stator winding MST to provide eight pole excitation of the winch motor as previously described. At the same time relay BR engages contacts BR3 to cause energization of the release coil of the electromechanical brake. Thus, the brake is released and the winch motor is started in the direction to lower the hook. Switch DF, upon operation, also engages contacts DFI, DFZ, DF3 and DF4 which, as previously described, causes the operation of accelerating switches AA, BA, CA and DA in sequence. This causes the short-circuiting in steps of rotor resistanc RR to cause the motor to operate at normal full speed.

Switch DF, upon operation, also engages contacts DF5 which completes a circuit for the coil of auxiliary direction switch X. This circuit is through contacts Zl, coil of switch X, contacts DF5, contacts CFZ and contact GI, switch G being operated as a result of the engagement of contacts BR4, as previously described. Switch X, upon operation, separates contacts X4 in the circuit for the coil of down direction switch D, this coil being maintained energized, however, through contacts DFT of the down auxiliary fast speed switch.

Switch DA, upon operation to short-circuit the remaining portion of rotor resistance RR, also engages contacts D.A5 to complete a circuit from master switch contact MD3 for the coil of auxiliary fast speed switch BF. Switch BF, upon operation, separates contacts BFI in the circuit for the coil of auxiliary fast speed switch AF. Assuming that the hook is empty, upon the winch motor coming up to full speed, the load switch contact LM is disengaged from a stationary contact so that the circuit for the coil of auxiliary fast speed switch AF is broken. Upon dropping out, switch AF breaks the circuit for the coils of the accelerating switches and for the coil of normal speed switch NS, as previously described. Switch NS, upon dropping out, breaks the circuits for causing eight pole excitation by stator winding MST. At the same time it engages contacts NS'I to complete a circuit for the coil of fast speed switch FS which operates as previously described to engage contacts FSI, FSZ and FS3 to reconnect stator winding MST to supply lines to cause four pole excitation of the winch motor. This brings the motor from normal operating speed up to fast speed.

Assume that instead of the hook being empty it has a heavy load. This is an over-hauling load on the winch motor, causing it to pump back into the supply lines to maintain its speed Slightly above synchronous speed for eight pole excitation. Due to the over-hauling load the load switch rotor is rotated in the opposite direction to that for lifting a heavy load. In accordance with the previous assumption, it will cause contact LM to be engaged with stationary contact LY. Thus although switch BF operates to separate contact BFi, contact LM remains in engagement with contact LY after the winch motor acceleration on eight pole excitation has been completed so that the circuit for the coil of auxiliary fast speed switch AF is not broken and the winch motor does not change over to fast speed operation.

Should master switch segment MS be moved only so far as contact MD2 in starting the motor, the circuit for the coil of switch BF is not completed so that change-over from normal to 'fast speed operation cannot be made regardless of the load being lowered. The Winch motor is not normally started to lower the hook from a high position by moving the master switch segment only into its first operative position bridging contact MDI with contact MDF, this operative position being provided for inching the load as it is about to be landed.

While the winch motor during downward movement of the hook may be slowed down and stopped in steps, it will be assumed that the master switch segment is returned directly to off position. Assurne first a condition in which the hook is empty and the winch motor is operating at fast speed. Under such conditions, auxiliary fast speed switch CF is operated, as previously described, so that contacts CF3 are in engagement to maintain the coil of down direction fast speed switch energized with the master switch segment in off position. The coil of switch X is energized through resistance RH after the separation of contacts CFZ, maintaining the switch operated. The disengagemer t of the master switch segment from contact MD3 breaks the circuit for the coils of auxiliary fast speed switch BF and fast speed switch PS. This results in the reoperation of switch AF and switch NS to restore the circuits for winch motor stator winding MST to provide eight pole excitation, as previously described. As a result, the winch motor is slowed down by regenerative braking. Also the accelerating switches are reopera-ted, as previously described, to provide the required slow down torque.

Upon the dropping out of switch CF after the breaking of its circuit by the separation of contacts F54 and the discharge of condenser C3 sufiiciently to permit the switch to dropout, contacts CF3 separate to break the circuit for the coils of switches DF and D. Switch D, upon dropping out, engages contacts D3 completing a circuit for the coils of relay SA and switch U. This, circuit is through contacts DiAd, CA5, BAE, coil of relay SA, contacts X3, coil of switch U and contacts D3. Switch D also separates contacts DI and D2 in the circuits for stator winding MST. However, contacts U1 and U2 engage to reestablish the circuits for stator winding MST, but reversing the connections from supply lines II and III. This plugs the, winch motor causing further slow down. Relay SA operates, as previously described, to render through th operation of relay S the coil of governor switch G subject to the voltage of the phase wound rotor winding. As the rotor winding voltage approaches zero, switch G drops out to break the circuit for the coil of switch X which in turn drops out separating contacts X3 to break the circuit for the coils of relay SA and switch U. Switch U, upon dropping out, separates contacts UI and U2 to deenergize stator winding MST and also separates contacts U5 to break the circuit for the coil of relay BR. Relay BR, upon dropping out, causes deenergization of the electromechanical brake so that the brake is applied to bring the Winch motor to a stop.

When the winch motor is lowering a loaded hook it is usually desirable to effect a landing of the load either on a platform at the wharf or at one of the ships decks, In such event, while the master switch segment may be centered and then moved back into position to engage contact MDI for an inching operation after the winch motor comes to a stop, it is preferred to move the master switch segment into position so that it remains in engagement with contact MDI but is off contacts MDZ and MD3. Under such conditions, assume that the winch motor is operating at normal speed due to the fact that the hook has a heavy load. Switch CF is not operated so that the disengagement of segment MS from contact MD2 breaks the circuit for the coils of switches DF and D. Switch D, upon dropping out, breaks the circuit for stator winding MST and at the same time causes operation. of switch U to establish reverse connections for stator winding MST to plug the motor, as previously described. Also relay SA is operated, as previously described, to render through the operation of relay S the coil of switch G subject to the voltage of the phase wound rotor winding. As the rotor winding voltage approaches zero, switch G drops out to break the circuit for the coil of switch X which in turn drops out to break the circuit for the coils of relay SA and switch U. Switch X also reengagcs contacts X4 which reestablishes the circuit from contacts MDI of the master control switch for the coil of switch D. Switch D, upon operation, separates contacts D4 breaking the circuit for the coil of normal speedswitch'NS which drops out to engage contacts NS6 completing a circuit from contact MDI of the master switch for the coil of slow speed switch SS- Thus, as up direction switch U and normal speed switch NS drop out to break the circuits for stator winding MST, down direction switch D and slow speed switch SS operate to engage contacts DI, D2, SS1 and SS2, establishing the circuits for slow speed stator winding MS-S for down direction of hook movement, thereby causing the hook to run at slow speed preparatory to landing the cargo. As the cargo lands, master switch segment MS is moved to ofi position which breaks the circuit for the coils of switches D and SS with the result that the circuits for the winch motor are broken and the brake is applied to bring the winch motor to a stop, contacts SS5 preventing delay in the dropping out of relay BR.

If during operation, the master switch is thrown from one operative position to another, the control system operates automatically to cause slow down of the motor and to start it in the opposite direction as it comes to a stop. Assume, for example, that the hook is being lifted and that the motor is operating at fast speed. Should the master switch segment MS be moved from position engaging contact MUG to position engaging contact M133, the circuit for the coils of switches BF and FS is broken as the master switch segment is disengaged from, contact MUG. Upon engagement of the segment with contact MD3 the circuit for these coils is not reestablished as contacts DA5 are separated preventing the energization of the coil of switch BF and as contacts BFZ and AFZ are separated preventing the energization of the coil of switch FS, switch AF being operated as the result of the engagement of contacts BFI. The engagement of contacts FSE and AFS complete a circuit for the coil of switch NS which establishes eight pole excitation of the motor to cause the motor to slow down by regenerative braking as previously described. Upon the dropping out of switch CF, switches DF and U are deenergized. This results in the operation of relay SA and switch D. Switch D acts to reverse the excitation of the motor, plugging the motor to cause further slow down. As the speed of the motor approaches zero, switch G drops out breaking the circuit for the coil of switch Z. Switch Z engages contacts Zl and Z3 to establish another circuit for the coil of switch D, the engagement of contacts Zl causing reoperation of switch DF. Thus the motor is caused to reverse and start in the down direction whereupon it is brought up to fast speed in the manner previously described. The operation of the system in case the master switch segment is moved from full down to full up position is similar and it is believed that this operation will be understood from the above description.

In review of the operation of the system, the hook may be raised by moving the master switch in the up direction. This causes the winch motor to start on eight pole excitation. Assuming that the master switch is moved to full on position, the rotor resistance is short-circuited in steps, this being the running condition of the motor circuits if a heavy load is being lifted. If the load is light, as the motor comes up to full speed on eight pole excitation it is automatically transferred to four pole excitation to double the operating speed. If the movement of the master switch in the up direction is short of full on position, the motor runs on eight pole excitation regardless of load. The speed of the motor on eight pole excitation may be varied by moving the master switch segment to different positions. Upon returning the master switch to off position to bring the motor to a stop, if operating at fast speed, the motor is first restored to eight pole excitation to cause slow down by regenerative braking, Then the excitation is reversed to plug the motor, causing further slow down. As the speed of the motor approaches zero, excitation of the motor is discontinued and the electromechanical brake is automatically applied to bring the motor to a stop.

The hook may be lowered by moving the master switch in the opposite direction. Assuming that it is moved to full on position, the winch motor starts on eight pole excitation and the rotor resistance is automatically short-circuited in steps. If the load on the hook is heavy, the motor remains on eight pole excitation, the over-hauling load causing the motor to pump back into the supply lines to maintain the speed slightly above synchronous speed. If the load is light, as the motor comes up to full speed on eight pole excitation it is automatically transferred to four pole excitation to double the operating speed. The master switch may be moved only to the second position if desired in which event the motor will operate on eight pole excitation regardless of the load on the hook. Upon returning the master switch to its first operating position, if operating at fast speed, the motor is first restored to eight pole excitation to cause slow down by regenerative braking. Then the excitation is reversed to plug the motor, causing further slow down. A the speed of the motor approaches zero, it is automatically transferred to thirty-six pole excitation to provide slow speed for inching in the down direction. As the load is landed, the master switch is returned to off position whereupon the electromechanical brake is applied to bring the motor to a stop. The master switch instead of being returned to its first operating position may be returned directly to off position. Then if it is desired to inch, the master switch is returned to the first position as the motor comes to a stop.

While the governor switch arrangement has been described as applied to a control system for a multi-speed alternating current cargo winch motor, it is adapted to various forms of motor control systems and may be utilized for various purposes. Many changes could be mad in the above construction and many apparently widely diiferent embodiments of this invention could be made without departing from the scope thereof, it is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.

What is claimed is:

1. A control system for a polyphase induction motor having a wound rotor comprising, a source of polyphase alternating current for said motor, a polyphase rectifier for deriving direct current from said source, a second polyphase rectifier for deriving direct current from said rotor and connected in series with the first named rectifier so that the direct current voltages thereof are in opposition, potentiometer resistance having a portion thereof connected across the first named rectifier and the remaining portion connected across the second rectifier, an electromagnetic switch having a single coil, and means connecting said coil across such portion of said potentiometer resistance that the voltage applied thereto is substantially zero with the motor connected to said source and at standstill.

2. A control system for a polyphase induction motor having a wound rotor comprising, a source of polyphas alternating current for said motor, a polyphase rectifier for deriving direct current from said source, a second polyphase rectifier for deriving direct current from said rotor and connected in series with the first named rectifier so that the direct current voltages thereof are in opposition, potentiometer resistance having a portion thereof connected across the first named rectifier and th remaining portion connected across said second rectifier, an electromagnetic switch having a single coil, means connecting said coil across such portion of said potentiometer resistance that the voltage applied thereto is substantially zero with the motor connected to said source and at standstill, and means for plugging said motor to cause slow down thereof thereby causing the voltage applied to said coil derived from said rotor to predominate and thus causing said switch to be in operated condition until the speed of said motor approaches zero.

3. A control system for a polyphase induction motor having a wound rotor comprising, a source of polyphase alternating current for said motor, a polyphase rectifier for deriving direct current from said source, a second polyphase rectifier for 15 deriving direct current from said rotor and connested in series with the first named rectifier so that the direct current voltages thereof are in opposition, potentiometer resistance having one portion thereof connected across the first named rectifier and the remaining portion connected across said second rectifier, an electromagnetic switch having a single coil, means adapted to connect said coil to such points on said potentiometer resistance that with the motor connected to said source and at standstill with one connection the potential drops across those parts of said resistance portions to which said coil is subject are neutralized and with another connection that due 16 to cause operation of said connecting means to establish said other connection for said coil to cause operation of said switch, means for plugging the said motor to cause slow down thereof, and means operable upon plugging the motor to cause operation of said connecting means to to said one connection therefor with reverse pochange from said other connection for said coil larity thereby causing sufiicient voltage to be applied to said 0011 due to the predominance of said potential drop due to said rotor to cause said switch to be operated, said switch dropping out as the speed of said motor approaches zero to decrease to zero the voltage applied to said coil as to said source predominates to cause sufficient 15 said potential drop due to said rotor decreases.

voltage to be applied to said coil for operating said witch, means operable in starting said motor JACOB DANIEL LEWIS. 

